Kisame still wins.... Mei is completely chakra based and unless her suiton contains more than 6 tailed beast tails of chakra nothing she has will touch him, while his speed and CQC abilities > hers
Kisame can absorb acid mist via samehada and skin and utilize multiple Mizu bunshins to distract Mei. Closing the distance is tough but Kisame could outlast Mei if he keeps a safe distance considering his speed allowed him to react o V1 Bee from a relatively close range which means suiton and lava are easily dodged at mid+ range.
As stated, Kisame should be able to handle all Mei's ninjutsu with Samehada. Even if she manages to miraculously damage him, he is extremely durable with that regeneration of his. Kisame low to mid-difficulty.
Welll you restricted Kisame's greatest skill. Without it he can't defeat Mei, well he can but only if he starts close to her to murk her in CQC with superior skill, strength and the Samehada.